1. Field of the Invention
The present invention relates to an image sensor unit and an image reader capable of reading image information, such as an image scanner, a facsimile, or a copying machine.
2. Description of the Related Art
Hitherto, various types of devices capable of reading an image, such as an image scanner, a facsimile, and a copying machine, have been proposed. There is, for example, one type having a relatively simple structure. In the structure, an image sensor unit, which can detect an image occupying up to the entire width of an original, is disposed parallel to an original-holding glass member. The image sensor unit is moved by an amount equal to the length of the original in order to scan the entire surface of the original. Various types of image sensor units have also been, hitherto, proposed. In one main type of image sensor unit, the original is illuminated by an illuminating member with a size equal to the width of the original. The light, reflected from the original, is guided to an image-focusing lens by a mirror in order to focus an image, which is reduced in size, on a line sensor, such as a charge-coupled device (CCD). In another main type of image sensor unit, the original is similarly illuminated by a light-emitting diode (LED) or the like. The light, reflected from the original is focused, with a magnification of 1x, on a light-receiving surface of the line sensor with a length equal to the width of the original, by a selfoc lens.
A description will now be given of a conventional image reader and an image sensor unit thereof, with reference to FIGS. 16 to 19. FIG. 16 is a front view of the conventional image reader. FIG. 17 illustrates the conventional image reader, as viewed from above the conventional image reader. FIG. 18 is an enlarged front view of the main portion of the conventional image reader. FIG. 19 illustrates the image sensor unit of the conventional image reader.
In the image reader, an original-holding glass member 101, for placing thereon an original, is disposed at the top portion of the body of the image reader. A line sensor unit 102, serving as an image sensor unit for reading the image on the original, is disposed below the original-holding glass member 101. The line sensor unit 102 comprises component parts that are integrally formed together into a unit. They are a light-emitting diode (LED) for illuminating an original; a selfoc lens array for focusing an image light reflected from the original illuminated by the light-emitting diode; and an optical sensor element for converting the image focused by the selfoc lens array into electrical signals. The line sensor unit 102 is secured to a sensor-holding frame 103 with screws, after positioning the line sensor unit 102 and the sensor-holding frame 103 by fitting pins 102a and 102b, at the bottom surface of a housing of the line sensor unit 102, into respective holes in the sensor-holding frame 103. The sensor-holding frame 103 is rotatably held by a moving holding frame 104, after fitting holes 104a and 104b, disposed at both ends of the moving holding frame 104, onto rotational shaft portions 103a and 103b, disposed at both ends of the sensor-holding frame 103 in a longitudinal direction thereof. The positioning of the sensor-holding frame 103 and the moving holding frame 104, in the longitudinal direction of the line sensor unit 102, is achieved by fitting a protrusion 103c of the sensor-holding frame 103 to a groove 104c in the moving holding frame 104. The moving holding frame 104 is guided by a guide bar 106 affixed to a body base 105. Coil springs 107a and 107b are provided at the sensor-holding frame 104, and bias the sensor-holding frame 103 towards the original-holding glass member 101. Two sliding protrusions 120a and 120b are affixed to the sensor-holding frame 103. The distance between the line sensor unit 102 and the original-holding glass member 101 is maintained by the sliding protrusions 120a and 120b that are in contact with the original-holding glass member 101. Such a structure, in which sliding protrusions are in contact with an original-holding glass member, is particularly suitable for use in small image sensor units with a small depth of field, and allows the distance between the original-holding glass member and the protrusions to be maintained with a relatively high precision. The driving of the moving holding frame 104 is achieved by causing a motor 109, an idler gear 121, and an idler gear 122 to drive a belt 112 and a pair of pulleys 110 and 111, and by linking one portion of the belt 112 to the moving holding frame 104. The belt 112 and the pair of pulleys 110 and 11 are provided at the body of the image reader in the direction of movement of the moving holding frame 104. The motor 109 is affixed to the body of the image reader.
The above-described conventional image sensor unit is a substantially rectangular parallelepipedic unit. In order to form the above-described high-precision supporting structure for the image sensor unit 102, the image sensor unit 102 is temporarily secured to the sensor-holding frame 103; a rotary mechanism is provided between the sensor holding frame 103 and the moving holding frame 104; a sliding protrusion is formed on the sensor holding frame 103; and a member, for positioning the image sensor unit 102 in the longitudinal direction thereof, is provided between the sensor-holding frame 103 and the moving holding frame 104. Therefore, when such a conventional image sensor unit is used in an image reader, a large space must be provided around the image sensor unit, thereby increasing the size of the image reader. In addition, a sensor-holding member is required, thereby increasing costs. Further, since part tolerances accumulate during incorporation of the image sensor unit into the image reader, the precision of the image reader is reduced accordingly.